5.3
筛分分析和级配曲线
筛分分析是一种用于确定骨料颗粒尺寸分布的方法。此过程涉及以下步骤:
- 称量所需数量的干燥骨料样品。
- 将称量的骨料通过一组方形开口的筛子进行筛选，这些筛子按孔径大小从大到小的顺序排列，最大的网眼位于顶部（表 1 的第 1 列）。
- 摇晃或振动筛堆，以便根据大小对颗粒进行分类。
- 筛分一定时间后，对每个筛子上…
采用一组筛子自上而下按筛孔尺寸从大到小叠放，对集料进行筛分分析。
粗骨料和细骨料所用筛子的尺寸各不相同。
称取一份风干的团聚体样品，通过机械或手动方式振荡筛分一段规定时间。
在此过程中，每个筛子会截留比其筛孔尺寸更粗的颗粒，同时允许更细的颗粒通过并进入下一个筛子。
记录每个筛子上截留的组分重量，以总质量的百分比表示，并以表格形式呈现。
从最细的筛子开始，依次向上计算通过每个筛子的累计百分比，并将结果四舍五入至最接近的整数百分比。
此外，采用半对数坐标图来表示通过百分比（y 轴）和筛孔尺寸（对数刻度的 x 轴）。
在此图中，绘制出每个筛孔尺寸对应的累计通过百分比，以获得级配曲线，该曲线表示集料颗粒基于其尺寸的分布情况。
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Q1: How is sieve analysis performed on aggregate samples?
Sieve analysis begins with weighing an air-dried aggregate sample, then passing it through a stack of sieves arranged in descending order of aperture size from top to bottom. The sieves are shaken mechanically or manually for a specified time, allowing finer particles to pass through while coarser particles are retained. The weight of material retained on each sieve is recorded and expressed as a percentage of total mass.
Q2: What is the purpose of calculating cumulative percentage passing in sieve analysis?
Cumulative percentage passing is calculated from the finest sieve moving upward to establish the foundation for grading curve development. This calculation, rounded to the nearest one percent, represents the proportion of aggregate particles finer than each sieve size. These values are plotted on the y-axis of a semi-logarithmic graph to visualize particle size distribution.
Q3: Why is a semi-logarithmic graph used to represent grading curves?
A semi-logarithmic graph is used because sieve apertures are plotted on a logarithmically scaled x-axis while cumulative passing percentages are plotted linearly on the y-axis. This scaling approach effectively displays the wide range of aggregate particle sizes and produces a grading curve that clearly indicates the distribution of particles across different size ranges.
Q4: What information does a grading curve provide about aggregates?
A grading curve visually simplifies the distribution of particle sizes within an aggregate sample by plotting cumulative passing percentages against sieve apertures. This graphical representation is essential for ensuring that aggregates meet required grading specifications for construction projects and helps engineers assess whether the material is suitable for specific applications.
Q5: How do sieve sizes differ between coarse and fine aggregates?
Sieve sizes vary for coarse aggregates and fine aggregates to accommodate their different particle size ranges. Coarse aggregates require larger mesh openings, while fine aggregates use smaller mesh sizes. The specific sieve stack selected depends on the aggregate classification and the particle size distribution being analyzed.
Q6: What does the weight retained on each sieve represent in sieve analysis?
The weight retained on each sieve represents the mass of particles coarser than that sieve's mesh size. This weight is recorded after sieving and then expressed as a percentage of the total sample mass. These percentages are essential for calculating cumulative passing values and constructing the grading curve.
Q7: Why must aggregate samples be air-dried before sieve analysis?
Air-drying the aggregate sample ensures consistent and accurate results by removing surface moisture that could affect particle behavior during sieving. Moisture can cause particles to clump together or stick to sieves, leading to incorrect weight measurements and inaccurate particle size distribution data.